This application claims the priority of Korean Patent Application No. 2003-44250, filed on Jul. 1, 2003 and No. 2004-11330, filed on Feb. 20, 2004, in the Korean Intellectual Property Office, the disclosures of these documents are incorporated herein in their entirety by reference.
1. Field of the Invention
The present invention relates to a projection optical system including a color filter layer, a projection television adopting the projection optical system, and a method of manufacturing a lens included in the projection optical system.
2. Description of the Related Art
FIG. 1 is a cross sectional view of a projection lens system of a color television disclosed in U.S. Pat. No. 5,055,922. Referring to FIG. 1, the projecting lens system 10 includes a fixing device 12 fixed to a cathode ray tube (CRT) 9. The fixing device 12 forms an enclosure 13 that holds a coolant.
The projection lens system 10 includes a first lens 14, a second lens 15, a third lens 16, a fourth lens 17, and a fifth lens 18 arranged sequentially, each of which partially corrects aberration. The first lens 14 has a low magnification and aspherical surfaces on both sides. The first lens 14 may be composed of acryl. The second lens 15 is a biconcave lens composed of polyethylene plastics and partially corrects chromatic aberration. The third lens 16 is a power lens providing most of the magnification of the projection optical system and may be composed of glass. The fourth lens 17 is a correction lens and may be composed of acryl plastics. The fourth lens 17 may have aspherical surfaces on both sides to correct aberration and may have low magnification. The fifth lens 18, which is a field flattener, is used with a coolant and may be composed of acryl plastics.
When the CRT 9 is a green CRT, the fifth lens 18 acts as a color filter containing a color filtering material that transmits a green beam with a 550 nm wavelength and absorbs beams at other wavelengths.
It is suggested that one of the other lenses besides the fifth lens 18 may be a color filter. A lens acting as a color filter may be formed by spreading a color filtering material on the entire inner surface of the lens. Here, to homogenize chromatic purity, the lens must be manufactured with a uniform thickness by injection molding, which, however, increases the possibility of configuration error and increases manufacturing costs. Further, the configuration of the projection optical system becomes complicated because a lens acting as a color filter is additionally added to the projection optical system.